The present invention relates to hydraulic pumps and in particular to such a pump having an integral sump and accumulator and adapted for use in anti-lock braking systems.
A source of pressurized braking fluid is an essential element in contemporary anti-lock braking systems. In one type of anti-lock braking system, a motor driven pump provides a source of pressurized braking fluid to increase braking pressure during a brake pressure build cycle, this type of system commonly being referred to as a full power system. In other systems, commonly referred to as pump-back systems, pressurized braking fluid is produced by the vehicle's power boosted master cylinder and a motor driven pump is utilized to replenish fluid lost from the vehicle's hydraulic circuits during brake pressure reduction or decay cycles. In both types of systems, it has been the common practice to provide the motor driven pump, a sump, and an accumulator as separate components. Such an arrangement possesses all of the inherent disadvantages of additional hydraulic connections, increased component count, added space requirements, reduction in hydraulic system stiffness, and the like. There therefor exists a need to provide an improved hydraulic pump system particularly well adapted for use in anti-lock braking systems which reduces or obviates the disadvantages of utilizing separate components for the pump, sump, and accumulator. It will also be recognized that such a system is equally applicable to traction control systems, that is, systems in which the brakes are utilized to reduce wheel spin during acceleration.
Broadly, the present invention is an integrated motor driven hydraulic pump, sump, and accumulator assembly which incorporates a pump body having a bore therein, pump piston means, a sump piston means, and an accumulator piston means disposed in the bore, a wall member fixedly mounted in the bore, and arranged such that the wall member, pump piston means, sump piston means, and accumulator piston means define therebetween variable volume pump, sump, and accumulator chambers, respectively. Motor driven means are provided for reciprocating the piston to pump fluid from the sump to the accumulator and valve means are provided within the wall member for controlling the flow of hydraulic fluid from the sump to the pump and accumulator chambers.
In one embodiment of the invention, a closure means is provided for closing the open end of the bore, the accumulator piston means and the closure member defining therebetween a variable volume accumulator pre-charged chamber. Preferably, the sump piston is hollow and the pump piston is axially reciprocally received therein. Accumulator and sump piston position switches may also be provided in the pump body.
It is therefor an object of the invention to provide an improved hydraulic pump assembly for use in anti-lock and traction control systems.
It is another object of the invention to provide such a system axially received within a common body and, in conjunction with a wall member, defines variable volume pump, sump, and accumulator chambers.
Still another object of the invention is to provide such an assembly in which all of the valves required for controlling the flow of hydraulic fluid are provided within the wall member.
Yet another object of the invention is to provide such a pump system in which all hydraulic connections between sump, pump, and accumulator are provided internally of the assembly.
Another object of the invention is to provide such an assembly requiring fewer parts, fewer hydraulic connections, and in which all hydraulic connections are of minimal length.
Yet another object of the invention is to provide such a pump system well adapted for mass production at minimal cost.